net: skb_copy_datagram_from_iovec()

There's an skb_copy_datagram_iovec() to copy out of a paged skb, but
nothing the other way around (because we don't do that).

We want to allocate big skbs in tun.c, so let's add the function.
It's a carbon copy of skb_copy_datagram_iovec() with enough changes to
be annoying.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 91 insertions, 0 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 358661c9990e..909923717830 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1452,6 +1452,10 @@ extern int	       skb_copy_datagram_iovec(const struct sk_buff *from,
 extern int             skb_copy_and_csum_datagram_iovec(struct sk_buff *skb,
                                                         int hlen,
                                                         struct iovec *iov);
+extern int             skb_copy_datagram_from_iovec(struct sk_buff *skb,
+                                                    int offset,
+                                                    struct iovec *from,
+                                                    int len);
 extern void            skb_free_datagram(struct sock *sk, struct sk_buff *skb);
 extern int             skb_kill_datagram(struct sock *sk, struct sk_buff *skb,
                                          unsigned int flags);
diff --git a/net/core/datagram.c b/net/core/datagram.c
index dd61dcad6019..52f577a0f544 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -339,6 +339,93 @@ fault:
         return -EFAULT;
 }
 
+/**
+ *      skb_copy_datagram_from_iovec - Copy a datagram from an iovec.
+ *      @skb: buffer to copy
+ *      @offset: offset in the buffer to start copying to
+ *      @from: io vector to copy to
+ *      @len: amount of data to copy to buffer from iovec
+ *
+ *      Returns 0 or -EFAULT.
+ *      Note: the iovec is modified during the copy.
+ */
+int skb_copy_datagram_from_iovec(struct sk_buff *skb, int offset,
+                                 struct iovec *from, int len)
+{
+        int start = skb_headlen(skb);
+        int i, copy = start - offset;
+
+        /* Copy header. */
+        if (copy > 0) {
+                if (copy > len)
+                        copy = len;
+                if (memcpy_fromiovec(skb->data + offset, from, copy))
+                        goto fault;
+                if ((len -= copy) == 0)
+                        return 0;
+                offset += copy;
+        }
+
+        /* Copy paged appendix. Hmm... why does this look so complicated? */
+        for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
+                int end;
+
+                WARN_ON(start > offset + len);
+
+                end = start + skb_shinfo(skb)->frags[i].size;
+                if ((copy = end - offset) > 0) {
+                        int err;
+                        u8  *vaddr;
+                        skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
+                        struct page *page = frag->page;
+
+                        if (copy > len)
+                                copy = len;
+                        vaddr = kmap(page);
+                        err = memcpy_fromiovec(vaddr + frag->page_offset +
+                                               offset - start, from, copy);
+                        kunmap(page);
+                        if (err)
+                                goto fault;
+
+                        if (!(len -= copy))
+                                return 0;
+                        offset += copy;
+                }
+                start = end;
+        }
+
+        if (skb_shinfo(skb)->frag_list) {
+                struct sk_buff *list = skb_shinfo(skb)->frag_list;
+
+                for (; list; list = list->next) {
+                        int end;
+
+                        WARN_ON(start > offset + len);
+
+                        end = start + list->len;
+                        if ((copy = end - offset) > 0) {
+                                if (copy > len)
+                                        copy = len;
+                                if (skb_copy_datagram_from_iovec(list,
+                                                                 offset - start,
+                                                                 from, copy))
+                                        goto fault;
+                                if ((len -= copy) == 0)
+                                        return 0;
+                                offset += copy;
+                        }
+                        start = end;
+                }
+        }
+        if (!len)
+                return 0;
+
+fault:
+        return -EFAULT;
+}
+EXPORT_SYMBOL(skb_copy_datagram_from_iovec);
+
 static int skb_copy_and_csum_datagram(const struct sk_buff *skb, int offset,
                                       u8 __user *to, int len,
                                       __wsum *csump)